Category Communication

What were various telecommunication modes?

 

TELECOMMUNICATIONS

Telecommunications is the sending and receiving of information using electricity, radio waves or light. The information can be sound, television pictures or computer data (which itself can be numbers, words, sounds and images). Forms of telecommunications include the telephone, fax, two-way radio, television and radio broadcasting, and the Internet. Most of these forms of communication require transmitting and receiving machines, and a network to link them together.

The first telecommunications device was the telegraph. Messages travelled along wires from a sending device to a receiving device as pulses of electricity, using some sort of code that both the sender and receiver understood. Practical telegraph systems were developed in the first half of the nineteenth century, and were first used for railway signalling. Early systems needed several connecting wires, but the system that eventually became standard, developed in the USA by Samuel Morse, needed just one wire. A network of telegraph lines, including undersea cables across the Atlantic, was quickly established right around the world.

In the early 1900s the telegraph was automated so that machines turned the message into code and back again. The sender could type messages on a keyboard and they would be printed out at the receiver’s end. To send a telegraph message, people had to visit a telegraph office. The message arrived at another office and was delivered by hand to the recipient.

The next major step in the development of telecommunications was the invention of the telephone, which could transmit speech, allowing people far apart to talk to each other. The first telephone receiver (the part that you talk into and listen to) was patented in 1876 by Alexander Graham Bell. This device both turned the sound of the user’s voice into an electrical signal, and an incoming signal into sound, which meant that the user could not talk and listen at the same time.

When the telephone was invented, there was no telephone network to link telephones in different places, but one soon grew up. All the telephone lines in an area meet at a telephone exchange, where they can be connected to one another, or to a line to another area’s exchange. The first exchange, opened in 1878 in Connecticut, USA, had just 21 lines. Like all early exchanges, it was operated by hand. A subscriber had to tell the operator which line he or she wanted to be connected to. The automatic exchange, which allowed people to dial numbers, was invented in the USA by Almon Strowger, and started working in 1897. Meanwhile, complex telephone networks grew in large cities. It took longer for different cities and countries to be linked, and until the middle of the twentieth century, the telegraph was still used for long-distance communication.

HOW A TELEPHONE WORKS

All telephone receivers are linked to a telephone exchange by a telephone line. When you lift or turn on the receiver, electronic circuits at the exchange detect it and wait for a number to be dialled. As you dial the number, the receiver sends signals to the exchange, which uses them to make a connection to the line of the person you are calling. The exchange makes the other telephone ring, and when it is answered, it connects the two lines together.

When you speak into the receiver’s mouthpiece, the sound makes a thin metal plate called a diaphragm vibrate. This movement affects the strength of an electric current, creating an electrical copy of the sound, which is called a signal. The signal travels through the connections in the telephone network to the other receiver, where it operates a tiny speaker in the earpiece, recreating the sound.

The signal travels in digital form for most of its journey through the network.

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What are Electromagnetic Radiations?

ELECTROMAGNETIC RADIATION

Radio waves, microwaves, light and X-rays have different characteristics, but they are all forms of electromagnetic radiation. Together with other forms, they make up a family called the electromagnetic spectrum. These forms of radiation can also be thought of as waves moving through space, in the same way as waves move across the surface of water. They all travel at the speed of light. Forms of electromagnetic radiation can be grouped according to their wavelengths – the distance between one wave crest and the next.

In reality, the wavelength at the left-hand end of the spectrum is a million million million times the wavelength at the right-hand end.

RADIO WAVES

The longest waves of the electromagnetic spectrum are radio waves. They have wavelengths ranging from more than 100 kilometres down to less than a metre. Radio waves are produced when an electric current changes strength or direction. Radio waves are important in communications through air and space. Microwaves are high-frequency radio waves also used in communications. Some microwave frequencies can be used in cooking.

Electromagnetic waves have amplitude and a frequency. Amplitude is the height or strength of a wave. Frequency is the number of wave crests that pass a point every second. To make a radio wave carry sound, it has to be modulated. This can be done by modulating (varying) either the strength of a wave – amplitude modulation or AM – or the speed of a wave – frequency modulation or FM.

LIGHT

In the middle of the electromagnetic spectrum is a small group of waves that our eyes detect, which is called visible light. It has wavelengths of around a thousandth of a millimetre. Waves with slightly different wavelengths appear as different colours, which together make up the colour spectrum. Light and especially laser light is very important in modern communications. Where practical, it is used in place of electricity and radio waves, because it can carry far more information without problems of interference.

 

INFRARED AND ULTRAVIOLET

To the left of visible light on the spectrum is infrared (IR) radiation. This is the radiation you feel as heat from hot objects. It is one of ways in which heat energy travels. Infrared radiation is used for short-range communications, such as in television remote controls, video camera autofocus and remote locking in cars.

To the right of visible light on the spectrum is ultraviolet (UV) radiation. It carries more energy than visible light. Ultraviolet radiation from the Sun is mostly absorbed by the atmosphere, but it still causes tanning of the skin and sunburn.

X-RAYS AND GAMMA RAYS

To the right of ultraviolet radiation are two more forms of electromagnetic radiation – X-rays and gamma rays. They both have very short wavelengths (less than a millionth of a millimetre) and extremely high frequencies (more than a million million million cycles per second). This means that X-rays and gamma rays have extremely high energies, and they can pass right through some solids. This makes them useful for investigating what is inside solid objects, such as human bodies, or closed suitcases at an airport security checkpoint.

X-rays were discovered by the German physicist Wilhelm Rontgen in 1895. They have a wide range of applications. In medicine, they are used to see the structure of bones and other organs by placing the patient between an X-ray source and a photographic film or camera. X-rays and gamma rays are also used in radiotherapy for treating cancers. However, in high doses they can damage tissues. X-rays are given off by high-energy, distant objects in space. X-ray telescopes can detect them.

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HOW DOES A TELEPHONE WORK?

A telephone works by sending and receiving electrical signals that represent sounds, including the human voice. When the required number is dialled, a signal passes to the called telephone, causing it to ring, buzz, flash a light, or even vibrate to attract the attention of the person using it. When the telephone is picked up or switched on, a connection is made, and a conversation can take place.

Messages reach the right telephone by means of a dialled number. Pressing the keys of the telephone causes different electrical pulses or varying tones to pass to electronic equipment at the telephone exchange. This “reads” the pulses or tones and routes the call to the correct area and telephone.

The Transmitter of a telephone serves as a sensitive “electric ear.” It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum.” The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker’s voice.

Behind the diaphragm lies a small cup filled with tiny grains of carbon. The diaphragm presses against these carbon grains. Low voltage electric current travels through the grains. This current comes from batteries at the telephone company. The pressure on the carbon grains varies as sound waves make the diaphragm vibrate. A loud sound causes the sound waves to push hard on the diaphragm. In turn, the diaphragm presses the grains tightly together. This action makes it easier for the electric current to travel through, and a large amount of electricity flows through the grains. When the sound is soft, the sound waves push lightly on the diaphragm. In turn, the diaphragm puts only a light pressure on the carbon grains. The grains are pressed together loosely. This makes it harder for the electric current to pass through them, and less current flows through the grains.

Thus, the pattern of the sound waves determines the pressure on the diaphragm. This pressure, in turn, regulates the pressure on the carbon grains. The crowded or loose grains cause the electric current to become stronger or weaker. The current copies the pattern of the sound waves and travels over a telephone wire to the receiver of another telephone. For more modern phones that have a telephone answering service, the sound wave is captured on a recording device which allows for the operator of the phone to playback at a later time.

The Receiver serves as an “electric mouth.” Like a human voice, it has “vocal cords.” The vocal cords of the receiver are a diaphragm. Two magnets located at the edge of the diaphragm cause it to vibrate. One of the magnets is a permanent magnet that constantly holds the diaphragm close to it. The other magnet is an electromagnet. It consists of a piece of iron with a coil of wire wound around it. When an electric current passes through the coil, the iron core becomes magnetized. The diaphragm is pulled toward the iron core and away from the permanent magnet. The pull of the electromagnet varies between strong and weak, depending on the variations in the current. Thus, the electromagnet controls the vibrations of the diaphragm in the receiver.

The electric current passing through the electromagnet becomes stronger or weaker according to the loud or soft sounds. This action causes the diaphragm to vibrate according to the speaker’s speech pattern. As the diaphragm moves in and out, it pulls and pushes the air in front of it. The pressure on the air sets up sound waves that are the same as the ones sent into the transmitter. The sound waves strike the ear of the listener and he hears the words of the speaker.

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WHAT IS SEMAPHORE?

Semaphore is a means of signalling using pairs of flags. Different flag positions stand for different letters and numbers. Semaphore signals are useful when the signaller is within sight of the receiver of the message but too far away to call out. It was widely used between ships sailing near each other in the days before ship-to-ship radio.

In programming, especially in UNIX systems, semaphores are a technique for coordinating or synchronizing activities in which multiple processes compete for the same operating system resources. A semaphore is a value in a designated place in operating system (or Kernel) storage that each process can check and then change. Depending on the value that is found, the process can use the resource or will find that it is already in use and must wait for some period before trying again. Semaphores can be binary (0 or 1) or can have additional values. Typically, a process using semaphores checks the value and then, if it using the resource, changes the value to reflect this so that subsequent semaphore users will know to wait.

Semaphores are commonly used for two purposes: to share a common memory space and to share access to files. Semaphores are one of the techniques for interprocess communication (IPC). The C programming language provides a set of interfaces or “functions” for managing semaphores.

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HOW DO COMMUNICATION SATELLITES WORK?

The layer of the Earth’s atmosphere called the ionosphere can reflect some radio waves back to Earth. This is used for sending messages over fairly short distances, but for messages to travel further across the Earth, the radio signals can be bounced off a satellite, orbiting almost 36,000km (22,000 miles) above the Earth’s surface. Several satellites, in different orbits, are required to give coverage over the whole globe, and different satellites are used to reflect signals for different media, such as telephone messages and television pictures.

A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals through a transponder. It basically creates a communication channel between a source transmitter and a receiver at different locations on earth. Communications satellites are used for television, telephone, radio, internet, and military applications. There are currently 2,134 communications satellites in the earth’s orbit and these comprise both private and government organizations. Several are in geostationary orbit 22,236 miles (35,785 km) above the equator, so that the satellite appears stationary at the same point in the sky. The orbital period of these satellites is the same as the rotation rate of the Earth, which in turn allows the satellite dish antennas of ground stations to be aimed permanently at that spot; they do not have to move along and track it. Since the high frequency radio waves used for telecommunications links travel by line of sight, they get obstructed by the curve of the earth. What these communications satellites do is they relay the signal around the curve of the earth thus making possible communication between widely removed geographical points. Communications satellites use a wide range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations stating which frequency ranges (or bands) certain organizations are permitted to use. This allocation of bands reduces the chances of signal interference.

A group of satellites working together is called a satellite constellation. Two such constellations are supposed to offer satellite phone services (mainly to remote areas), are the Iridium and Global star systems. The Iridium system has 66 satellites. It is also possible today to provide discontinuous coverage using a low-earth-orbit satellite that can store data received while passing over one part of earth and transmitting it later while passing over another part. The CASCADE system being used by Canada’s CASSIOPE communications satellite is an apt example.

A satellite in orbit has to operate continuously over its entire life span. It needs internal power to be able to operate its electronic systems and communications payload. The main source of power is sunlight, which is harnessed by the satellite’s solar panels. A satellite also has batteries on board to provide power when the Sun is blocked by Earth. The batteries are recharged by the excess current generated by the solar panels when there is sunlight.

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HOW HAVE MODERN COMMUNICATIONS CHANGED OUR LIVES?

Modern communications have affected our lives in numerous ways. Being able to pass information down telephone wires or via satellites means that some people can work from anywhere in the world and still keep in constant touch with their offices. A surgeon in Arizona, via a satellite link, can assist a colleague in Beijing with a complicated operation. News can travel halfway around the world as quickly as it can reach the next town. Perhaps the biggest effect of communications has been to make us all feel that the world is a smaller place, and that we need to be concerned about its future and the futures of people thousands of miles away.

The Internet has turned our existence upside down. It has revolutionized communications, to the extent that it is now our preferred medium of everyday communication. In almost everything we do, we use the Internet. Ordering a pizza, buying a television, sharing a moment with friend, sending a picture over instant messaging. Before the Internet, if you wanted to keep up with the news, you had to walk down to the newsstand when it opened in the morning and buy a local edition reporting what had happened the previous day. But today a click or two is enough to read your local paper and any news source from anywhere in the world, updated up to the minute.

Technology has improved communication, especially in recent years. We’ll always have so much information readily available at our fingertips. Writing letters to relatives living hundreds of miles away is so old-school! Instead, you can talk to them through a video call or instant messaging. This change in communication has completely changed relationships all over the world.

Services like Facebook and Twitter have also become a big part of our everyday lives. These sites allow people to see a lot of information and photos at once and are enjoyable by design. When you upload a photo to the Internet, it doesn’t simply go away. It stays for a long time. This means you can use technology to store memories that are important to you, like family photos.

With modern technology, we can live much healthier lives. Those who have fitness trackers can see how active they are. Seeing that can encourage us to be even more active. Some fitness trackers like the Apple Watch even gamify health with competitions and points!

New technology can help create cures and medicines. Someone who is sick in modern times is much more likely to be cured than someone in past times. Modern technology can automate just about anything, from turning on a light to ordering a pizza. With automation, we can do so much more in such a small amount of time. For example, you can use your voice to start the coffee maker while you’re still getting dressed.

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